The present invention relates to an optical signal processor for dropping from or adding to an optical transmission line a signal at any one of a plurality of specific wavelengths.
In dense wavelength division multiplexer (WDM) optical transmission systems a multiplicity of optical signals is transmitted, each at a different wavelength. One or more of the signals is dropped off and/or added at a system node. The component forming the node should add as little loss as possible to the system, be highly reliable, and be actively switchable. It is also desirable that one or any combination of wavelengths be added or dropped at each node. Such components would be extremely useful for the 1530-1560 nm Er amplification passband.
It is well known that an add/drop multiplexer/demultiplexer (A/D M/D) component 10 can be fabricated by assembling a Bragg grating (BG) device 12 tuned to the desired wavelength .lambda..sub.i with two circulators 14, 16 as shown in FIG. 1. Bragg grating devices can be implemented in various forms including fiber and planar devices. Each of the circulators described herein includes ports 1, 2 and 3. The circulators can be replaced by 3 dB couplers as discussed below. Component 10 receives a composite group of signals of different wavelengths .lambda..sub.a -.lambda..sub.k on input line 11 and provides the desired multiplexed signal of wavelength .lambda..sub.i on WDM output line 18. The term "line" is used to mean optical fiber or planar optical path, depending upon how the component is constructed. The remaining signals from line 11, except for that at wavelength .lambda..sub.i, are transmitted to output line 20. An input signal of wavelength .lambda..sub.i that appears at line 19 is combined with those remaining signals at output line 20. However, component 10 is not switchable. It can be made to drop multiple wavelengths by adding additional gratings between the circulators, but signals at all wavelengths that are reflected by the gratings must be dropped at the WDM output line 18.